“Salmon occupy an important place in the food web,” said NOAA Fisheries’ Mary R. Arkoosh, a supervisory research microbiologist and lead author of a new paper on dietary exposure to a binary mixture of polybrominated diphenyl ethers (PDBE). “For example, small juvenile Chinook salmon in Puget Sound feed on plankton while larger juvenile Chinook salmon feed on herring and other fish, and Chinooks themselves are prey items for endangered southern resident killer whales.”
Researchers are interested in identifying the causes contributing to the decline of these fish, Arkoosh said. “We determined that PBDE exposure in Chinook alters thyroid levels and immune function as well as an impaired the ability of these salmon to fight off a disease.”
“Contaminants that increase disease susceptibility have the potential to influence population numbers of endangered or threatened salmonids,” Arkoosh said. “Even a modest reduction in first year mortality, on the order of 10 percent during juvenile residence in either the river or the estuary ecosystem, can lessen current population declines of Chinook salmon. Therefore, even a small reduction in disease resistance due to chemical exposure can potentially have a significant impact on salmonid population,” she said.
The research results, which were published online by Elsevier, also notes that the researchers examined how juvenile Chinooks exposed to PBDEs responded to bacteria that are capable of killing them. They found that exposed salmon had reduced survival rates and that the response was complex. The function of macrophages, a critical cell of the immune system in fish, was also examined.
Researchers found that macrophages from juvenile Chinooks exposed to PBDEs did not function as macrophages do from fish not exposed to it. “This change in function of an important immune cell may impact the ability of Chinook to defend themselves against disease.” Arkoosh noted.
Results of this work at NOAA Fisheries’ Northwest Fisheries Science Center in Seattle, Wash., have been used in conjunction with monitoring studies to determine the proportion of salmon in Puget Sound that had levels of PBDEs that may impact the endocrine and immune system. The hope is that genetic studies now underway will help determine if other physiological systems may be impacted in Chinooks from exposure to PBDEs.